Devices of this type are commonly used for coupling an implement to an agricultural or industrial tractor, truck or other utility vehicle. The implement may generally be a machine which is towed or supported by the tractor. An example of a towed implement might be a plow or trailer. A supported implement might comprise, a sprayer for example. Particular implements which might be employed are plows, sowing machines, balers, and mowing machines. Various attachment interfaces (also called hitches) are known, for attaching an agricultural implement to an agricultural utility vehicle. Such a coupling apparatus is, for example a three-point hitch, as defined by German Standard DIN 9674 (or ISO 730).
The article “Mechatronics in Mobile Hydraulics” (in German) (2002 Landtechnik, 57, 3:140-141), discloses a hitch which is a refinement of the customary three-point hitch, wherein the lifting thrust elements and the upper link bar are in the form of length-adjustable elements.
If the upper link bar is switched into a pressureless state, a “tipping” movement between the implement and the working vehicle, around an axis which essentially passes through the articulation points on the side directed toward the implement, can be achieved. The axis of tipping is always disposed in or on the implement, as a consequence of the configurational design, in the customary hitches. This means that the tipping axis is far from an axle of the working vehicle, in particular far from the rear axis of the working vehicle. As a result, a supported load from the implement acting on the working vehicle is transmitted to the working vehicle via a moment arm which extends from the working vehicle axle (e.g. the rear working vehicle axle) to the tipping axis. This is disadvantageous from the standpoint of force transmission, particularly transmission of supported loads from the implement to the working vehicle, because it diminishes the load on the other axle of the working vehicle (e.g. the front axle). This load reduction needs to be compensated for by a counterweight. Such an approach is costly and consumptive of resources, because different implements will exert different supported loads on the working vehicle, necessitating the positioning of different counterweights on the working vehicle in order to achieve optimum weight distribution between the axles of the working vehicle. This requirement is particularly burdensome for working vehicles in the form of agricultural tractors, because these generally require good contact between all of the wheels and the ground.
The term “tipping” in the context of the present invention refers to any movement around an essentially horizontally disposed axis which is essentially perpendicular to the longitudinal axis of the hitch, when the equipment is in operating position.
The underlying problem of the present invention is deemed to be to devise an apparatus for coupling an implement to a working vehicle, the apparatus being of the general type described hereinabove, with improvements such that the above-described drawbacks are overcome. In particular, the system should not be such that a supported load from the implement acting on the working vehicle will unavoidably diminish the load on one of the axles of the working vehicle.